Method and Apparatus of Forming Cracks as Masks for the Fabrication of Micro-Metal Mesh

ABSTRACT

Methods and systems for forming cracks as masks for the fabrication of micro-metal mesh are disclosed, including depositing a composite film onto a substrate wherein the composite film comprises a brittle layer, a brittle layer atop a mediate layer, or a brittle layer atop a sacrificial layer; generating a tensile stress in the substrate and/or the composite film in order to form micro-cracks in the brittle layer; tuning widths of the micro-cracks; transferring pattern of the micro-cracks onto the sacrificial layer; depositing a conductive material onto the brittle layer and the area of the substrate or mediate layer exposed by the pattern of the micro-cracks; and performing a lift-off of the brittle layer and if present the sacrificial layer from the substrate or mediate layer, resulting in the micro-metal mesh atop the substrate or mediate layer. Other embodiments are described and claimed.

I. BACKGROUND

The invention relates generally to the field of forming cracks as masksfor the fabrication of micro-metal mesh. More particularly, theinvention relates to a roll-to-roll compatible method and apparatus offorming cracks in a deposition layer for the fabrication of micro-metalmesh.

II. SUMMARY

In one respect, disclosed is a method for fabricating a micro-metalmesh, the method comprising: depositing a brittle layer onto asubstrate; generating a tensile stress in the substrate and/or thebrittle layer in order to form micro-cracks in the brittle layer; tuningwidths of the micro-cracks; depositing a conductive material onto thebrittle layer and the area of the substrate exposed by the pattern ofthe micro-cracks; and performing a lift-off of the brittle layer fromthe substrate, resulting in the micro-metal mesh atop the substrate.

In another respect, disclosed is a method for fabricating a micro-metalmesh, the method comprising: depositing a mediate layer onto asubstrate; depositing a brittle layer onto the mediate layer; generatinga tensile stress in the substrate, the mediate layer, and/or the brittlelayer in order to form micro-cracks in the brittle layer; tuning widthsof the micro-cracks; depositing a conductive material onto the brittlelayer and the area of the mediate layer exposed by the pattern of themicro-cracks; and performing a lift-off of the brittle layer from themediate layer, resulting in the micro-metal mesh atop the mediate layer.

In another respect, disclosed is a method for fabricating a micro-metalmesh, the method comprising: depositing a sacrificial layer onto asubstrate; depositing a brittle layer onto the sacrificial layer;generating a tensile stress in the substrate, the sacrificial layer,and/or the brittle layer in order to form micro-cracks in the brittlelayer; tuning widths of the micro-cracks; transferring pattern of themicro-cracks onto the sacrificial layer; depositing a conductivematerial onto the brittle layer and the area of the substrate exposed bythe pattern of the micro-cracks transferred onto the sacrificial layer;and performing a lift-off of the sacrificial layer and the brittle layerfrom the substrate, resulting in the micro-metal mesh atop thesubstrate.

In yet another respect, disclosed is an apparatus for formingmicro-cracks in a brittle layer, the apparatus comprising: a rollerhaving a diameter; the apparatus configured to: drive a composite filmaround the roller to generate a tensile stress in the composite film,wherein the composite film comprises the brittle layer atop a substrate;and form cracks in the brittle layer, wherein the cracks are parallel tothe axis of the roller and have a period dependent on the diameter ofthe roller.

Numerous additional embodiments are also possible.

III. BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention may become apparent uponreading the detailed description and upon reference to the accompanyingdrawings.

FIGS. 1A and 1B are pictures of a metal mesh and a nanowire network,respectively.

FIGS. 2A, 2B, 2C, and 2D are cross-sectional illustrations of the stepsin fabricating a micro-metal mesh, in accordance with some embodiments.

FIG. 3 is a top-view illustration of the periodic metal nanowirestructure illustrated in FIG. 2D, in accordance with some embodiments.

FIG. 4 is a top-view illustration of a metal nanowire mesh, inaccordance with some embodiments.

FIG. 5 is a top-view illustration of a metal nanowire mesh, inaccordance with some embodiments.

FIGS. 6A, 6B, 6C, and 6D are cross-sectional illustrations of the stepsin fabricating a micro-metal mesh, in accordance with some embodiments.

FIG. 7 is a top-view illustration of the periodic metal nanowirestructure illustrated in FIG. 6D, in accordance with some embodiments.

FIG. 8 is a cross-sectional view illustration of a roller setup used togenerate cracks in a brittle layer, in accordance with some embodiments.

FIG. 9 is a block diagram illustrating a method for forming cracks asmasks for the fabrication of a micro-metal mesh, in accordance with someembodiments.

FIG. 10 is a block diagram illustrating a method for forming cracks asmasks for the fabrication of a micro-metal mesh, in accordance with someembodiments.

FIGS. 11A, 11B, 11C, 11D and 11E are cross-sectional illustrations ofthe steps in fabricating a micro-metal mesh, in accordance with someembodiments.

FIG. 12 is a top-view illustration of the random metal mesh structureillustrated in FIG. 11E, in accordance with some embodiments.

FIG. 13 is a block diagram illustrating a method for forming cracks asmasks for the fabrication of a micro-metal mesh with a bi-layercomposite film, in accordance with some embodiments.

While the invention is subject to various modifications and alternativeforms, specific embodiments thereof are shown by way of example in thedrawings and the accompanying detailed description. It should beunderstood, however, that the drawings and detailed description are notintended to limit the invention to the particular embodiments. Thisdisclosure is instead intended to cover all modifications, equivalents,and alternatives falling within the scope of the present invention asdefined by the appended claims.

IV. DETAILED DESCRIPTION

One or more embodiments of the invention are described below. It shouldbe noted that these and any other embodiments are exemplary and areintended to be illustrative of the invention rather than limiting. Whilethe invention is widely applicable to different types of systems, it isimpossible to include all of the possible embodiments and contexts ofthe invention in this disclosure. Upon reading this disclosure, manyalternative embodiments of the present invention will be apparent topersons of ordinary skill in the art.

Transparent conductors are structures and materials that areelectrically conductive and optically transparent or translucent.Transparent conductors are an essential part in many electronic devices,such as touch panels, flat screen displays, light emitting diodes, andsolar cells and also in other applications such as in transparentheaters and in electromagnetic (EM) shielding. Presently, Indium TinOxide (ITO) is one of the prevailing materials used as transparentconductors in electronic devices. However, due to ITO's brittleness,high cost, high optical diffraction index, limited conductivity, andlimited transparency, alternatives to the use of ITO are desirable.Alternatives such as metal mesh, metal nanowire, graphene, and carbonnanotube have attracted attention as alternatives to ITO. Of thesealternatives, metal mesh and metal nanowire networks are especiallyattractive due to their excellent combination of high conductivity andhigh transparency.

FIGS. 1A and 1B are pictures of a metal mesh and a nanowire network,respectively.

FIG. 1A shows a typical metal mesh network manufactured by Unipixel,Inc. (www.unipixel.com). Unipixel utilizes an additive manufacturingprocess where micron sized copper lines 105 are printed on flexibleprinted electronics. The micron sized metal lines 105 are difficult tofabricate and relatively expensive to implement. FIG. 1B shows a typicalnanowire network manufactured by Cambrios Technologies Corporation(www.cambrios.com). Cambrios utilizes a directly patternable,wet-processable transparent conductive film made from silver nanowires110 to produce a network of nanowires to form a metal mesh. Althoughwith the Cambrios nanowire network, narrow metal lines as narrow as 100nm are possible, the tunable range of conductivity and transparency arerelatively limited. Additionally, the Cambrios nanowire network isrelatively expensive to implement. What is needed is a method offabricating a metal mesh that is made up with metal lines that can betuned with line widths between 20 nm to 5 μm and where the periodicityof the metal lines can also be tuned between 500 nm to 1 mm. A method offabricating such a micro-metal mesh is disclosed in this invention.

FIGS. 2A, 2B, 2C, and 2D are cross-sectional illustrations of the stepsin fabricating a micro-metal mesh, in accordance with some embodiments.

In some embodiments, a brittle layer 205 is deposited onto a substrate210 as illustrated in FIG. 2A. The brittle layer 205 may comprisespin-on-glass, liquid glass, ceramic, salt, carbon, and/or polymethylmethacrylate (PMMA). The substrate 210 may comprise any transparent andflexible film, such as polyethylene terephthalate (PET), polyimide (PI),cellulose, polyester, polyethylene, polyolefin, polycarbonate, flexibleglass, or a combination or lamination thereof. A tensile stress may begenerated in the brittle layer during its deposition or in a subsequentprocess such as during the heating, curing, or chemical crosslinking ofthe brittle layer. Next, micro-cracks 215 are generated in the brittlelayer 205. Various methods, such as mechanical bending, stretching,squeezing, pressing, thermal shock, and quenching, may be used togenerate micro-cracks 215 in the brittle layer 205 as shown in FIG. 2B.The micro-cracks 215 are generated as a result of the stress in thesubstrate 210 and the brittle layer 205. The density of the micro-cracksis determined by the stress in the brittle layer. The size of themicro-cracks may be adjusted by adjusting the thermal processingparameters, such as the drying temperature, the drying speed, and/or thedrying time, or by etching. The width of the micro-cracks may range fromabout 20 nm to about 5 μm. Micro-cracks may also be generated in thebrittle layer by adding nanoparticles in the brittle layer. Thenanoparticles may comprise silver, copper, gold, iron, nickel, cobalt,platinum, palladium, titanium, aluminum, chromium, and/or molybdenum.After the micro-cracks have been generated, a layer of conductivematerial 220, comprising metals, alloys, and/or doped semiconductor, isdeposited onto the micro-cracked brittle layer 205 as shown in FIG. 2C.The brittle layer with the micro-cracks is used as a mask during thedeposition of the conductive material. Next, the brittle layer islifted-off resulting in a structure of metal nanowires 225 atop thesubstrate 210 as illustrated in the periodic, one-dimensional metalnanowires 223 of FIG. 2D. FIG. 3 shows the top view of the periodicmetal nanowire structure 225, comprising four one-dimensional metalnanowires 223, atop the substrate 210 as shown in FIG. 2D. In order tofabricate a two-dimensional metal nanowire mesh, a two-dimensional cracknetwork may be generated in the step shown in FIG. 2B or in thealternative, the process steps as shown in FIG. 2A to FIG. 2D may berepeated but with a different orientation of the substrate. FIG. 4illustrates a two-dimensional metal nanowire mesh network 405 where thecracks were substantially orthogonal to each other. Other morecomplicated metal nanowire mesh networks may be generated by usingadditional micro-crack directions. FIG. 5 illustrates a metal nanowiremesh 505 where the cracks were substantially sixty degrees relative toeach other.

FIGS. 6A, 6B, 6C, and 6D are cross-sectional illustrations of the stepsin fabricating a micro-metal mesh, in accordance with some embodiments.

In some embodiments, in order to control a larger range in the widths ofthe generated cracks, a mediate layer 602 is deposited onto a substrate610, followed by the deposition of a brittle layer 605 onto the mediatelayer 602 as illustrated in FIG. 6A. The more flexible and elasticmediate layer 602 relaxes the stress which is used to generate thecracks in the brittle layer 605. The mediate layer 602 may comprisePMMA, PS, polyvinyl chloride (PVC), rubber, silicone,polydimethylsiloxane (PDMS), nylon, or a combination thereof. Thebrittle layer 605 may comprise spin-on-glass, liquid glass, ceramic,salt, carbon, and/or PMMA. The substrate 610 may comprise anytransparent and flexible film, such as PET, PI, cellulose, polyester,polyethylene, flexible glass, and/or other similar materials. A tensilestress may be generated in the brittle layer during its deposition or ina subsequent process such as during the heating, curing, or chemicalcrosslinking of the brittle layer. Next, micro-cracks 615 are generatedin the brittle layer 605. Various methods, such as mechanical bending,stretching, squeezing, pressing, thermal shock, and quenching, may beused to generate micro-cracks 615 in the brittle layer 605 as shown inFIG. 6B. The micro-cracks 615 are generated as a result of the stress inthe substrate 610, the mediate layer 602, and the brittle layer 605. Thesize of the micro-cracks is tunable by adjusting the stress in thebrittle layer 605, the mediate layer 602, and/or the substrate 610.After the micro-cracks have been generated, a layer of conductivematerial 620, comprising metals, alloys, and/or doped semiconductor, isdeposited onto the micro-cracked brittle layer 605 as shown in FIG. 6C.The brittle layer with the micro-cracks is used as a mask during thedeposition of the conductive material. Next, the brittle layer islifted-off resulting in a structure of metal nanowires 625 atop themediate layer 602 as illustrated in the periodic, one-dimensional metalnanowires 623 of FIG. 6D. FIG. 7 shows the top view of the periodicmetal nanowire structure 625, comprising four one-dimensional metalnanowires 623, atop the mediate layer 602 as shown in FIG. 6D. In orderto fabricate a two-dimensional metal nanowire mesh, similar to thetwo-dimensional metal nanowire mesh networks illustrated in FIG. 4 andFIG. 5, a two-dimensional crack network may be generated in the stepshown in FIG. 6B or in the alternative, the process steps as shown inFIG. 6A to FIG. 6D may be repeated but with a different orientation ofthe substrate.

FIG. 8 is a cross-sectional view illustration of a roller setup used togenerate cracks in a brittle layer, in accordance with some embodiments.

In some embodiments, an apparatus 800 comprises a mechanical bendingused to generate the micro-cracks. A composite film 801 comprising abrittle layer 805 and a substrate 810 is wrapped around a roller 815 asillustrated in FIG. 8. The roller 815 has a diameter D. The compositefilm may be driven by the roller 815 or by an external roll-to-rollmechanical system (not shown). As the composite film is driven aroundthe roller 815 in the direction shown by arrows 820 and 825, cracks 830are formed in the brittle layer 805. The cracks 830 run along and areparallel to the axis 835 of the roller 815. The period between cracks Pmay be tuned by changing the diameter D of the roller 815. The largerthe diameter D, the larger the period P between cracks. The compositefilm may also comprise a mediate layer or a sacrificial layer betweenthe brittle layer and the substrate, resulting in a periodic crackstructure as shown and described in FIGS. 6D and 11E, respectively. Inorder to fabricate more complicated metal nanowire, two-dimensional meshnetworks, a two-dimensional micro-crack network may be generated bydriving the composite film around the roller again but with a differentorientation of the substrate. After formation of the periodic crackstructure by wrapping the composite film around the roller, the widthsof the cracks 830 may be tuned by adjusting the stress in the compositefilm. The stress may be adjusted by adjusting the thermal processingparameters, such as the drying temperature, the drying speed, and/or thedrying time, or by etching. In an embodiment with a sodium silicidebrittle layer, the width of the crack may be adjusted from 20 nm to 1mm.

In one embodiment, a brittle layer of spin-on-glass, such as P-102Fspin-on-glass from Filmtronics, was spun onto a substrate of cleaned PETfilm at a thickness between 75 μm to 100 μm using a rotation rate of1,000 rpm for 40 seconds. The composite film of the spin-on-glass atopthe PET film was subsequently dried in order to induce a tensile stress.The composite film may be dried at room temperature for a longer time oron a hot plate for shorter time. If dried at room temperature, thecomposite film is dried for two hours. Next, the dried composite film ismechanically bent at a constant stress of 2 MPa with rollers havingdifferent diameters. The diameter of the roller controls the periodbetween cracks. For roller diameters of 1.6 mm, 2.4 mm, 3.2 mm, 4 mm,4.8 mm, 5.6 mm, 10 mm, and 30 mm, periods of 500 nm-5 μm, 7 μm, 10 μm,15 μm, 20 μm, 30 μm, 200 μm, and 1 mm were formed, respectively. Therange of periods from 500 nm to 5 μm for the 1.6 mm diameter roller wasachieved by adjusting the stress in the composite film during thethermal drying process of the composite film. After formation of theperiodic crack structure by wrapping the composite film around theroller, the widths of the cracks may be tuned by adjusting the stress inthe composite film. The stress may be adjusted by adjusting the thermalprocessing parameters, such as the drying temperature, the drying speed,and/or the drying time, or by etching. The annealing may comprise atemperature ranging from about 40° C. to about 180° C. and a timeranging from about 10 seconds to about 1 hour. Using baking temperaturesof 60° C., 80° C., 100° C., 110° C., 120° C., 130° C., 140° C., and 150°C. resulted in crack widths of 20 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400nm, 500 nm, 700 nm, and 1000 nm, respectively.

FIG. 9 is a block diagram illustrating a method for forming cracks asmasks for the fabrication of a micro-metal mesh, in accordance with someembodiments. In some embodiments, the method illustrated in FIG. 9 maybe performed by the device illustrated in FIG. 8.

Processing begins at 900 whereupon, at block 905, a brittle layer isdeposited onto a substrate to form a composite film. In someembodiments, the brittle layer may comprise spin-on-glass, liquid glass,ceramic, salt, carbon, and/or PMMA and the substrate may comprise anytransparent and flexible film, such as PET, PI, cellulose, polyester,polyethylene, flexible glass, and/or other similar materials. At block910, a tensile stress is generated in the brittle layer and/orsubstrate. Depending on the brittle layer used, a tensile stress may begenerated in the brittle layer during its deposition or in a subsequentprocess such as heating, curing, or chemical crosslinking of the brittlelayer. Next, at block 915, micro-cracks are generated in the brittlelayer. A one dimensional and/or two-dimensional micro-crack network maybe generated by mechanical bending, stretching, squeezing, pressing,thermal shock, and/or quenching. After the micro-cracks have beenformed, at block 920, the width of the micro-cracks may be tuned byadjusting the thermal processing parameters, such as the dryingtemperature, the drying speed, and/or the drying time, or by etching.The width of the micro-cracks may range from about 20 nm to about 5 μm.Next, at block 925, a conductive material is deposited onto thecomposite film. The brittle layer with the micro-cracks is used as amask during the deposition of the conductive material. The conductivematerial may comprise metals, alloys, and/or doped semiconductor. Atblock 930, the brittle layer is lifted-off from the substrate resultingin a metal nanowire structure atop the substrate. The metal nanowirestructure may comprise periodic, one-dimensional metal nanowires and/ora two-dimensional metal nanowire mesh with line widths between about 20nm to about 5 μm with a spacing between metal lines between about 500 nmto about 1 mm. Processing subsequently ends at 999.

FIG. 10 is a block diagram illustrating a method for forming cracks asmasks for the fabrication of a micro-metal mesh, in accordance with someembodiments. In some embodiments, the method illustrated in FIG. 10 maybe performed by the device illustrated in FIG. 8.

Processing begins at 1000 whereupon, at block 1005, a mediate layer isdeposited onto a substrate. In some embodiments, the mediate layer maycomprise rubber, silicone, PDMS, and/or silicone rubber and thesubstrate may comprise any transparent and flexible film, such as PET,PI, cellulose, polyester, polyethylene, flexible glass, and/or othersimilar materials. Next, at block 1010, a brittle layer is depositedonto the mediate layer to form a composite film comprising the brittlelayer, the mediate layer, and the substrate. The brittle layer maycomprise spin-on-glass, liquid glass, ceramic, salt, carbon, and/orPMMA. At block 1015, a tensile stress is generated in the brittle layer,the mediate layer, and/or the substrate. Depending on the brittle layerand mediate layer used, a tensile stress may be generated in the brittlelayer and mediate layer during its deposition or in a subsequent processsuch as heating, curing, or chemical crosslinking of the brittle layerand mediate layer. Next, at block 1020, micro-cracks are generated inthe brittle layer. A one dimensional and/or two-dimensional micro-cracknetwork may be generated by mechanical bending, stretching, squeezing,pressing, thermal shock, and/or quenching. After the micro-cracks havebeen formed, at block 1025, the width of the micro-cracks may be tunedby adjusting the thermal processing parameters, such as the dryingtemperature, the drying speed, and/or the drying time, or by etching.The width of the micro-cracks may range from about 20 nm to about 5 μm.Next, at block 1030, a conductive material is deposited onto thecomposite film. The brittle layer with the micro-cracks is used as amask during the deposition of the conductive material. The conductivematerial may comprise metals, alloys, and/or doped semiconductor. Atblock 1035, the brittle layer is lifted-off from the mediate layerresulting in a metal nanowire structure atop the mediate layer. Themetal nanowire structure may comprise periodic, one-dimensional metalnanowires and/or a two-dimensional metal nanowire mesh with line widthsbetween about 20 nm to about 5 μm with a spacing between metal linesbetween about 500 nm to about 1 mm. Processing subsequently ends at1099.

FIGS. 11A, 11B, 11C, 11D and 11E are cross-sectional illustrations ofthe steps in fabricating a micro-metal mesh with bi-layer compositefilm, in accordance with some embodiments.

In some embodiments, a sacrificial layer 1115 is deposited onto asubstrate 1110, followed by the deposition of a brittle layer 1105 ontothe sacrificial layer 1115 as illustrated in FIG. 11A. The sacrificiallayer 1115 may be, but not limited to nylon and/or photo resists such asShipley S1800 series. The thickness of sacrificial layer 1115 rangesfrom about 50 nm-1000 nm. The brittle layer 1105 may comprisespin-on-glass, liquid glass, ceramic, salt, carbon, and/or PMMA. Thesubstrate 1110 may comprise any transparent and flexible film, such asPET, PI, cellulose, polyester, polyethylene, flexible glass, and/orother similar materials. Next, micro-cracks 1120 are generated in thebrittle layer 1105. Various methods, such as mechanical bending,stretching, squeezing, pressing, thermal shock, quenching and addingnanoparticles in the brittle layer 1105, may be used to generatemicro-cracks 1120 in the brittle layer 1105 as shown in FIG. 11B. Thesize of the micro-cracks is tunable by adjusting the thermal processingparameters after cracks are generated, such as the drying temperature,the drying speed, and/or the drying time, or by etching. The pattern ofthe micro-cracks 1125 in the sacrificial layer is copied or transferredby partially dissolving and/or reactive ion etching the uncovered areaof the sacrificial layer 1115 as shown in FIG. 11C. After themicro-cracks 1125 have been generated, a layer of conductive material1130, comprising metals, alloys, and/or doped semiconductor, isdeposited onto the composite film as shown in FIG. 11D. Next, thebi-layer, comprising the brittle layer 1105 and the sacrificial layer1115, is lifted-off resulting in a structure of micro-mesh 1135 atop thesubstrate 1110 as illustrated in the FIG. 11E. FIG. 12 shows the topview of the micro-mesh structure 1135 atop the substrate 1110 as shownin FIG. 11E.

In one embodiment, a sacrificial layer of PMMA from MicroChem, is coatedonto a substrate of cleaned PET film at a thickness between 75 μm and150 μm by a micro-gravure roll-to-roll coater from MIRWEC Film, Inc.Next, a brittle layer of spin-on-glass, such as P-102F from filmtronic,is coated onto the PMMA film by the same roll-to-roll coater. Thecomposite film is subsequently dried in air at room temperature for 2hours. Next, the dried composite film is thermal shocked and annealed bybaking on a hot plate. The density of the micro-cracks increases whenthe baking temperature is increased from 50° C. to 150° C. The size ofthe micro-cracks increases from 200 nm to 700 nm when the baking time isincreased from 30 seconds to 3 minutes at 110° C. Next, the micro-crackspattern is copied to the PMMA layer by immersing the film in Acetone for10 seconds. Next, 100 nm of silver is deposited onto the micro-crackedcomposite film by e-beam evaporation or sputtering. Next, the PMMA andspin-on-glass layer bi-layer is lifted-off from the substrate resultingin a metal mesh structure atop the PET substrate.

FIG. 13 is a block diagram illustrating a method for forming cracks asmasks for the fabrication of a micro-metal mesh, in accordance with someembodiments. In some embodiments, the method illustrated in FIG. 13 maybe performed by the device illustrated in FIG. 8.

Processing begins at 1300 whereupon, at block 1305, a sacrificial layerand a brittle layer are deposited onto a substrate to form a compositefilm. In some embodiments, the sacrificial layer can be, but not limitedto polymers such as PMMA, PS, PVC, rubber, silicone, PDMS, nylon and/orphoto resists such as Shipley S1800 series. The brittle layer maycomprise spin-on-glass, liquid glass, ceramic, salt, carbon, and/or PMMAand the substrate may comprise any transparent and flexible film, suchas PET, PI, cellulose, polyester, polyethylene, flexible glass, and/orother similar materials. At block 1310, micro-cracks are generated byvarious methods, such as mechanical bending, stretching, squeezing,pressing, thermal shock, quenching and adding nanoparticles in thebrittle layer. After the micro-cracks have been formed, at block 1315,the width of the micro-cracks may be tuned by adjusting the annealingprocessing parameters, such as anneal temperature and time. The width ofthe micro-cracks may range from about 20 nm to about 5 μm. Then themicro-cracks pattern is transferred or copied to the sacrificial layerat block 1320. The pattern of the micro-cracks in the sacrificial layeris copied or transferred by partially dissolving and/or reactive ionetching the uncovered area of the sacrificial layer. Next, at block1325, a conductive material is deposited onto the composite film. Thebi-layer, comprising the sacrificial layer and the brittle layer, isused as a mask during the deposition of the conductive material. Theconductive material may comprise metals, alloys, and/or dopedsemiconductor having a material selected from the group consisting ofsilver, copper, gold, iron, nickel, cobalt, platinum, palladium,titanium, aluminum, chromium, molybdenum, or a combination thereof. Atblock 1330, the bi-layer is lifted-off from the substrate resulting in ametal mesh structure atop the substrate. The metal mesh structure has aline width between about 200 nm to 1000 nm with a spacing between metallines. Processing subsequently ends at 1399.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

The benefits and advantages that may be provided by the presentinvention have been described above with regard to specific embodiments.These benefits and advantages, and any elements or limitations that maycause them to occur or to become more pronounced are not to be construedas critical, required, or essential features of any or all of theclaims. As used herein, the terms “comprises,” “comprising,” or anyother variations thereof, are intended to be interpreted asnon-exclusively including the elements or limitations which follow thoseterms. Accordingly, a system, method, or other embodiment that comprisesa set of elements is not limited to only those elements, and may includeother elements not expressly listed or inherent to the claimedembodiment.

While the present invention has been described with reference toparticular embodiments, it should be understood that the embodiments areillustrative and that the scope of the invention is not limited to theseembodiments. Many variations, modifications, additions and improvementsto the embodiments described above are possible. It is contemplated thatthese variations, modifications, additions, and improvements fall withinthe scope of the invention as detailed within the following claims.

1. A method for fabricating a micro-metal mesh, the method comprising:depositing a mediate layer onto a substrate; depositing a brittle layeronto the mediate layer; generating a tensile stress in the substrate,the mediate layer, and/or the brittle layer in order to formmicro-cracks in the brittle layer; tuning widths of the micro-cracks;depositing a conductive material onto the brittle layer and the area ofthe mediate layer exposed by the pattern of the micro-cracks; andperforming a lift-off of the brittle layer from the mediate layer,resulting in the micro-metal mesh atop the mediate layer.
 2. The methodof claim 1, wherein tuning the widths of the micro-cracks comprisesetching the brittle layer or annealing the substrate, the mediate layer,and the brittle layer.
 3. The method of claim 2, wherein the annealingcomprises a temperature ranging from about 40° C. to about 180° C. 4.The method of claim 2, wherein the annealing comprises a time rangingfrom about 10 seconds to about 1 hour.
 5. The method of claim 1, whereinthe substrate comprises a transparent and flexible film having amaterial selected from the group consisting of polyethyleneterephthalate, polyimide, cellulose, polyester, polyethylene,polyolefin, polycarbonate, glass, or a combination or laminationthereof.
 6. The method of claim 1, wherein the brittle layer comprisesspin-on-glass, liquid glass, ceramic, salt, carbon, and/or PMMA.
 7. Themethod of claim 1, wherein the mediate layer comprises a materialselected from the group consisting of PMMA, PS, PVC, rubber, silicone,PDMS, nylon, or a combination thereof.
 8. The method of claim 1, whereinthe conductive material comprises a metal, alloy, and/or dopedsemiconductor having a material selected from the group consisting ofsilver, copper, gold, iron, nickel, cobalt, platinum, palladium,titanium, aluminum, chromium, molybdenum, or a combination thereof. 9.The method of claim 1, wherein the micro-cracks comprise a width rangingfrom about 20 nm to about 5 μm.
 10. The method of claim 1, whereingenerating a tensile stress comprises mechanical bending, stretching,squeezing, pressing, thermal shock, quenching, and/or addingnanoparticles in the brittle layer.
 11. The method of claim 10, whereinthe nanoparticles comprise silver, copper, gold, iron, nickel, cobalt,platinum, palladium, titanium, aluminum, chromium, and/or molybdenum.12. The method of claim 1, wherein the method is roll-to-rollcompatible.
 13. A method for fabricating a micro-metal mesh, the methodcomprising: depositing a sacrificial layer onto a substrate; depositinga brittle layer onto the sacrificial layer; generating a tensile stressin the substrate, the sacrificial layer, and/or the brittle layer inorder to form micro-cracks in the brittle layer; tuning widths of themicro-cracks; transferring pattern of the micro-cracks onto thesacrificial layer; depositing a conductive material onto the brittlelayer and the area of the substrate exposed by the pattern of themicro-cracks transferred onto the sacrificial layer; and performing alift-off of the sacrificial layer and the brittle layer from thesubstrate, resulting in the micro-metal mesh atop the substrate.
 14. Themethod of claim 13, wherein tuning the widths of the micro-crackscomprises etching the brittle layer or annealing the substrate, thesacrificial layer, and the brittle layer.
 15. The method of claim 14,wherein the annealing comprises a temperature ranging from about 40° C.to about 180° C.
 16. The method of claim 14, wherein the annealingcomprises a time ranging from about 10 seconds to about 1 hour.
 17. Themethod of claim 13, wherein transferring the pattern of the micro-cracksonto the sacrificial layer comprises dissolving and/or reaction ionetching the sacrificial layer exposed by the pattern of the micro-cracksin the brittle layer.
 18. The method of claim 13, wherein the substratecomprises a transparent and flexible film having a material selectedfrom the group consisting of polyethylene terephthalate, polyimide,cellulose, polyester, polyethylene, polyolefin, polycarbonate, glass, ora combination or lamination thereof.
 19. The method of claim 13, whereinthe brittle layer comprises spin-on-glass, liquid glass, ceramic, salt,carbon, and/or PMMA.
 20. The method of claim 13, wherein the sacrificiallayer comprises a polymer selected from the group consisting of PMMA,PS, PVC, rubber, silicone, PDMS, nylon, and photo resist.
 21. The methodof claim 13, wherein the conductive material comprises a metal, alloy,and/or doped semiconductor having a material selected from the groupconsisting of silver, copper, gold, iron, nickel, cobalt, platinum,palladium, titanium, aluminum, chromium, molybdenum, or a combinationthereof.
 22. The method of claim 13, wherein the micro-cracks comprise awidth ranging from about 20 nm to about 5 μm.
 23. The method of claim13, wherein generating a tensile stress comprises mechanical bending,stretching, squeezing, pressing, thermal shock, quenching, and/or addingnanoparticles in the brittle layer.
 24. The method of claim 23, whereinthe nanoparticles comprise silver, copper, gold, iron, nickel, cobalt,platinum, palladium, titanium, aluminum, chromium, and/or molybdenum.25. The method of claim 13, wherein the method is roll-to-rollcompatible.
 26. An apparatus for forming micro-cracks in a brittlelayer, the apparatus comprising: a roller having a diameter; theapparatus configured to: drive a composite film around the roller togenerate a tensile stress in the composite film, wherein the compositefilm comprises the brittle layer atop a substrate; and form cracks inthe brittle layer, wherein the cracks are parallel to the axis of theroller and have a period dependent on the diameter of the roller. 27.The apparatus of claim 26, wherein the composite film further comprisesa mediate layer or a sacrificial layer between the brittle layer and thesubstrate.
 28. The apparatus of claim 26, wherein the roller thediameter ranges from about 1.6 mm to about 30 mm.